I built a fighter subclass involving a fighter than can only use the one sword that is magically bonded to him/her. As the fighter levels up, the sword levels up as well, based on the monsters it kills. This subclass has some other abilities as well. What I'm really curious about is whether you fighter types can help me think of problems with this kind of a situation that fundamentally break the concept. Here's my rough draft of my fighter subclass, the Infernal Knight:
There exists a group of fighters who are willing to seek ultimate power at any cost. These fighters discovered long ago that the Nine Hells are full of devils willing and ready to grant them the power they seek in the form of a profane infernal weapon that hungers for the souls of those it slays. This weapon is said to grow in power along with its wielder as it kills more and stronger enemies. These fighters, bound by their damnation and the fiery weapons they wield, are known as Infernal Knights. Powerful Infernal Knights are capable of using their blades to inflict not only grievous physical damage to their foes, but also to channel the fires of hell itself through the blade using magical spells.
At Level 3, you perform a forbidden ritual, offering to trade your soul to a greater devil of the Nine Hells in exchange for increased combat power in your mortal life. There is always a devil waiting for such an offer who infuses its infernal essence into a beautifully-crafted longsword, which then appears before you. When you take the longsword in your hand and wield it for the first time, you are magically bonded to the weapon and the contract is sealed. After that point, if anyone else attempts to wield your bonded infernal blade, it is treated as a common nonmagical longsword... unless the fiend in the blade senses a darkness in the new wielder and decides to act upon it.
Once you are bonded to your infernal blade, It becomes the only melee weapon you are able to use.
You always have disadvantage when using any other melee weapon, regardless of other modifiers which may otherwise negate disadvantage.
As a bonus action, you may summon or dismiss your infernal blade to your hand. If you have no free hands, you drop at least one held item to make room for the blade.
While you are wielding your infernal blade, any creature you strike that is immune to slashing damage is treated as having resistance instead. This applies only to your attacks.
You may choose to wield your infernal blade in one hand or in both hands.
If you chose archery, great weapon fighting, or two weapon fighting as your fighting style at level 2, you may now change that selection one time only.
Though you have sold your mortal soul, revivify and other resurrection spells work as normal.
Each day at dawn, your infernal blade regains a number of charges equal to its blade level. These charges can be used like a wand to invoke various effects.
Absorb Soul
When you slay a creature, your infernal sword hungers to consume its soul. As an action, you may absorb the soul of a creature you slew within the last 1 minute. When you do this, you recover hit points equal to the CR of the creature you slew. Creatures with a CR less than 1 provide no healing. There is no limit to the number of souls your blade is capable of absorbing. Its hunger is insatiable. Constructs have no souls, so they may not be absorbed.
Blade Advancement
Your blade grows in power as you defeat stronger enemies. The level of your blade is equal to the CR of the strongest soul your infernal blade has absorbed. If you absorb the soul of a creature whose CR is higher than your character level, the sword matches your current character level until level 18, when the limit expires. As your blade grows in power, it becomes a more formidable weapon. Blade advancement follows the following table:
Blade Level
1h Base Damage
2h Base Damage
1
1d8
1d10
2
1d8
1d10
3
1d8
1d10
4
1d8
1d10
5
1d10
1d12
6
1d10
1d12
7
1d10
1d12
8
1d10
1d12
9
1d12
1d8+1d6
10
1d12
1d8+1d6
11
1d12
1d8+1d6
12
1d12
1d8+1d6
13
1d8+1d6
2d8
14
1d8+1d6
2d8
15
1d8+1d6
2d8
16
1d8+1d6
2d8
17
2d8
4d4
18
2d8
4d4
19
2d8
4d4
20
2d8
4d4
21
4d4
3d6
22
4d4
3d6
23
4d4
3d6
24
4d4
3d6
25
3d6
5d4
26
3d6
5d4
27
3d6
5d4
28
3d6
5d4
29
5d4
6d4
30
5d4
6d4
Devil's Sight
As your sword begins to grow in power, its dark gifts start to reveal themselves to you. As an action, you may spend 1 charge from your blade to invoke a limited version of Devil's Sight, meaning you can see normally in darkness, both magical and nonmagical, to a distance of 60 feet for 10 minutes.
Infernal Condition
You are bolstered by aspects of the devil within your blade. While you are wielding your infernal blade, you are resistant to fire damage, but you are vulnerable to radiant damage.
Bully
At level 7, you have started to come to terms with the powers of your blade and the effect it can have on you and on those around you. As an action, you may spend 1 charge from your blade to enhance the most sinister aspects of your appearance. You gain advantage on intimidation checks for 1 minute.
Hellfire Blade
At 7th level, your blade attacks are always considered magical for the purpose of overcoming damage resistance. As a bonus action, you may spend 2 charges from your blade to invoke an incantation that ignites your blade with infernal hellfire. On a successful hit, your blade does an additional 1d6 fire damage. This effect lasts for 1 minute.
Release Soul
At 10th level, you learn how to work with the souls of slain enemies absorbed into your sword. When you absorb a soul, you have 1 minute to touch an ally with your blade as an action and release the soul's energy into them as healing for hit points equal to the CR value of the absorbed soul. No soul under CR 1 provides any healing.
Hellfire Burst
At 15th level, you gain the ability to release an explosive burst of hellfire upon your enemies. As an action, you may spend 5 charges from your blade and point your blade to a location you can see within 150 ft and cause a fireball to explode there.
Infernal Magic
Starting at 18th level, you have access to some rudimentary fire magic. Though you are no spellcaster, your mind comprehends the methods of calling a fire shield or a wall of fire. As an action, you may spend 5 charges from your sword to cast either of these spells.
Your constructive criticism of the subclass itself is always welcome. I'm really looking for a horrible mechanical oversight I've created. I thank you for taking the time to help me out.
EDIT: I have modified a few details and reposted the most recent draft of this subclass.
Hey! not sure if this is too late, but I've got to say I really like the concept! It's got some good potential though there are a few things i think could be improved slightly I'll work through the draft in order:
At Level 3, you perform a forbidden ritual, offering to trade your soul to a greater devil of the Nine Hells in exchange for increased combat power in your mortal life. There is always a devil waiting for such an offer who infuses its infernal essence into a beautifully-crafted longsword, which then appears before you. When you take the longsword in your hand and wield it for the first time, you are magically bonded to the weapon and the contract is sealed. After that point, if anyone else attempts to wield your bonded infernal blade, it is treated as a common nonmagical longsword... unless the fiend in the blade senses a darkness in the new wielder and decides to act upon it.
The only real issue with this is that it seems like it limits the character too much to only use a longsword, it forces the player into a very narrow play style when compared to other sub-classes of fighter, perhaps changing it so that the character can repeat the ritual to transfer the devil into a new weapon. adding a time period for the ritual will help too, during a long rest should work fine. obviously allowing other weapons aside from longswords means that the damage scaling in the table will need to be very different, so you'd have to play around with different ways of getting it to work.
For the next bit I'll cross out ones i think you should remove and then highlight ones I think you should change, then I'll explain my choices:
Once you are bonded to your infernal blade, It becomes the only melee weapon you are able to use.
You always have disadvantage when using any other melee weapon, regardless of other modifiers which may otherwise negate disadvantage.
As a bonus action, you may summon or dismiss your infernal blade to your hand. If you have no free hands, you drop at least one held item to make room for the blade.
While you are wielding your infernal blade, any creature you strike that is immune to slashing damage is treated as having resistance instead. This applies only to your attacks.
You may choose to wield your infernal blade in one hand or in both hands.
If you chose archery, great weapon fighting, or two weapon fighting as your fighting style at level 2, you may now change that selection one time only.
Though you have sold your mortal soul, revivify and other resurrection spells work as normal.
Each day at dawn, your infernal blade regains a number of charges equal to its blade level. These charges can be used like a wand to invoke various effects.
OK so the first point ties into my initial one, so I'll skip that one.
My only real change I'd add here is just to add the word 'must' into the description:
As a bonus action, you may summon or dismiss your infernal blade to your hand. If you have no free hands, you must drop at least one held item to make room for the blade.
While you are wielding your infernal blade, any creature you strike that is immune to slashing damage is treated as having resistance instead. This applies only to your attacks.
For this one, the main issue is that it gets negated later on at 7th level, when the blade counts as being magical, since most creatures that are immune or resistant to slashing are only immune to slashing from non-magical attacks this becomes functionally useless. what you should do instead is to just make the weapon count as magical for the purposes of resistances. this is in line with stuff like the Warlock Pact of the Blade, in which pact weapons count as magical and is also a 3rd level ability so it isn't overpowered either.
You may choose to wield your infernal blade in one hand or in both hands.
If you chose archery, great weapon fighting, or two weapon fighting as your fighting style at level 2, you may now change that selection one time only.
Though you have sold your mortal soul, revivify and other resurrection spells work as normal.
the next few are ones I view as being mostly irrelevant, the properties of the longsword mean the first one is already covered in the item description and if you change the Infernal Knight to allow other weapons this becomes unnecessary. The second one clashes too much if only longswords are allowed, as the other fighting styles become useless, Fighters as a whole are designed to use a variety of weapons, the last one is also largely unnecessary, Paladin Deities and Warlock patrons don't restrict Resurrection, the DM can rule it as they like, but the base class shouldn't have to specify that resurrection works.
Absorb Soul
When you slay a creature, your infernal sword hungers to consume its soul.As an action, you may absorb the soul of a creature you slew within the last 1 minute. When you do this, you recover hit points equal to the CR of the creature you slew. Creatures with a CR less than 1 provide no healing. There is no limit to the number of souls your blade is capable of absorbing. Its hunger is insatiable. Constructs have no souls, so they may not be absorbed.
The main changes for this would be to make the absorption automatic, in combat having to use an action to absorb the soul is a bit of a waste. The Hexblade's Curse for Hexblade Warlocks handles healing by using the Warlock level and the charisma modifier, perhaps something similar might be better. except maybe Strength instead? The reason against using CR is that not everyone builds encounters around it, so people who don't use CR won't be able to use this class effectively;additionally the healing would be fairly weak if it's based on CR. Perhaps granting temporary hit points instead would be a wiser choice. Another option would be to take a set amount of hit points from the enemy for healing, such as a quarter, this is modelled of weapons like Blackrazor which have a similar ability, you could add that at higher levels it does a half instead of a quarter, so it scales nicer. since you won't necessarily be landing killing blows all the time it should be fair.
Blade Advancement
Your blade grows in power as you defeat stronger enemies. The level of your blade is equal to the CR of the strongest soul your infernal blade has absorbed. If you absorb the soul of a creature whose CR is higher than your character level, the sword matches your current character level until level 18, when the limit expires. As your blade grows in power, it becomes a more formidable weapon. Blade advancement follows the following table:
For this one I'll only cover the text here, the table requires some changes, if you allow for multiple weapons, perhaps the Monk damage table will give some ideas. I think perhaps an HP threshold will work better than a CR system, in addition to the aforementioned issues with CR for class mechanics, CR doesn't scale with individual character level, but for groups, so I think HP is a better indicator of a creature's strength, some high CR creatures are flimsy and are more glass cannons after all. this way there is not hard limit on how strong the sword gets. perhaps adding a flat damage bonus onto the sword that increases as it levels up:perhaps Intervals like: 3-5, 6-8, 9-11, 12-14, 14,15-17, 18-20, with +1d4, +1d6, +1d8,, +1d10, +1d12, etc, would work better?
This was just an example to illustrate the kind of stuff you could do, but it feels like a reasonable progression, play-testing is important here to see whether the level up is either too quick or too slow.
Devil's Sight
As your sword begins to grow in power, its dark gifts start to reveal themselves to you. As an action, you may spend 1 charge from your blade to invoke a limited version of Devil's Sight, meaning you can see normally in darkness, both magical and non-magical, to a distance of 60 feet for 10 minutes.
For this I think you just need to remove the highlighted phrase, perhaps you could also allow the ability to increase the range to 120 feet at higher levels? otherwise the player may feel like they don't get strong enough. additionally the level requirement for this isn't mentioned
Infernal Condition
You are bolstered by aspects of the devil within your blade. While you are wielding your infernal blade, you are resistant to fire damage, but you are vulnerable to radiant damage.
Same as before, the level requirement isn't mentioned. Additionally for some races this is just a straight nerf, certain dragonborn and Tieflings straight up just get a vulnerability, As far as resistances go fire is ok, but fairly common, so I think you could potentially completely rework this or remove it, maybe make the user resistant to charm effects instead? the user is already in the thrall of a devil after all.
Bully
At level 7, you have started to come to terms with the powers of your blade and the effect it can have on you and on those around you. As an action, you may spend 1 charge from your blade to enhance the most sinister aspects of your appearance. You gain advantage on intimidation checks for 1 minute.
I think a charge for only 1 minute of advantage on intimidation is a bit expensive, consider making it just a flat advantage on Intimidation, maybe Deception too? it matches the devilish themes pretty well. In fact depending on how you change the subclass it may be worth removing the charge system completely? it's up to you of course though.
Hellfire Blade
At 7th level, your blade attacks are always considered magical for the purpose of overcoming damage resistance. As a bonus action, you may spend 2 charges from your blade to invoke an incantation that ignites your blade with infernal hellfire. On a successful hit, your blade does an additional 1d6 fire damage. This effect lasts for 1 minute.
i think 2 charges or only 1d6 is a bit much, since the infernal blade damage will probably be weaker, it might be worth increasing the damage to 2d6? or decreasing the cost of the 1d6 damage to just 1 charge.
Release Soul
At 10th level, you learn how to work with the souls of slain enemies absorbed into your sword. When you absorb a soul, you have 1 minute to touch an ally with your blade as an action and release the soul's energy into them as healing for hit points equal to the CR value of the absorbed soul. No soul under CR 1 provides any healing.
This feels slightly out of place, it makes some sense with how the absorb souls works already, but I feel like this healing is a bit too weak for 10th level, maybe using healing like that for the Absorb Soul modifications would work slightly better. also it's unclear if passing the soul on removes the hit points healed by the Absorb Souls ability, does passing the hit points on transfer them from you to the other character? it is a bit ambiguous as is.
Hellfire Burst
At 15th level, you gain the ability to release an explosive burst of hellfire upon your enemies. As an action, you may spend 5 charges from your blade and point your blade to a location you can see within 150 ft and cause a fireball to explode there.
Infernal Magic
Starting at 18th level, you have access to some rudimentary fire magic. Though you are no spellcaster, your mind comprehends the methods of calling a fire shield or a wall of fire. As an action, you may spend 5 charges from your sword to cast either of these spells.
For these two I feel that infernal magic is fine, but 5 charges for a Fireball you only get at 15th level seems a bit much, I think 3 charges is more reasonable, otherwise you can only use that single fireball and nothing else. perhaps making the cost of charges equal the spell level is a fairer way? that means maybe adding a fifth level spell to the Infernal Magic, though that seems reasonable enough to me. also I think using the standard range of fireball is fine, no need to specify the range. one other thing to clarify is what is the Spellcasting DC for the Infernal Knight? Fireball requires a save and as such needs a spell-casting save. 8 + proficiency + constitution might be a good way to go.
Overall I like the flavour of the class and it looks fun to play!, feel free to completely disregard my post, but I also hope you keep it in mind.
No you're not too late at all. Unfortunately, you're replying to a (by this point) much older draft of my subclass. I have tweaked a lot of things... and then I came to the conclusion that as much as I liked it, it's just thematically too similar to a hexblade warlock. Some of the things that seemed less fighter-appropriate are holdovers from when the class was originally envisioned as a paladin subclass. I still have the subclass on the back burner, but I kept the core blade concept and I'm presently working with the blade as a magic item instead. I'll read over your thoughts again when I have a little more time to devote to it and I'll also share what I have, although think by this point, it's probably better suited to the homebrew forum than the fighter forum.
Most importantly, I appreciate you taking the time to look over it and I definitely appreciate your feedback.
After a lot of consideration, I have decided to abandon this concept as a subclass and instead, I turned it into a magic item. I felt like it was just too one-dimensional for a subclass, but I still enjoyed the mechanics of the blade itself.
I built a fighter subclass involving a fighter than can only use the one sword that is magically bonded to him/her. As the fighter levels up, the sword levels up as well, based on the monsters it kills. This subclass has some other abilities as well. What I'm really curious about is whether you fighter types can help me think of problems with this kind of a situation that fundamentally break the concept. Here's my rough draft of my fighter subclass, the Infernal Knight:
There exists a group of fighters who are willing to seek ultimate power at any cost. These fighters discovered long ago that the Nine Hells are full of devils willing and ready to grant them the power they seek in the form of a profane infernal weapon that hungers for the souls of those it slays. This weapon is said to grow in power along with its wielder as it kills more and stronger enemies. These fighters, bound by their damnation and the fiery weapons they wield, are known as Infernal Knights. Powerful Infernal Knights are capable of using their blades to inflict not only grievous physical damage to their foes, but also to channel the fires of hell itself through the blade using magical spells.
At Level 3, you perform a forbidden ritual, offering to trade your soul to a greater devil of the Nine Hells in exchange for increased combat power in your mortal life. There is always a devil waiting for such an offer who infuses its infernal essence into a beautifully-crafted longsword, which then appears before you. When you take the longsword in your hand and wield it for the first time, you are magically bonded to the weapon and the contract is sealed. After that point, if anyone else attempts to wield your bonded infernal blade, it is treated as a common nonmagical longsword... unless the fiend in the blade senses a darkness in the new wielder and decides to act upon it.
Absorb Soul
When you slay a creature, your infernal sword hungers to consume its soul. As an action, you may absorb the soul of a creature you slew within the last 1 minute. When you do this, you recover hit points equal to the CR of the creature you slew. Creatures with a CR less than 1 provide no healing. There is no limit to the number of souls your blade is capable of absorbing. Its hunger is insatiable. Constructs have no souls, so they may not be absorbed.
Blade Advancement
Your blade grows in power as you defeat stronger enemies. The level of your blade is equal to the CR of the strongest soul your infernal blade has absorbed. If you absorb the soul of a creature whose CR is higher than your character level, the sword matches your current character level until level 18, when the limit expires. As your blade grows in power, it becomes a more formidable weapon. Blade advancement follows the following table:
Devil's Sight
As your sword begins to grow in power, its dark gifts start to reveal themselves to you. As an action, you may spend 1 charge from your blade to invoke a limited version of Devil's Sight, meaning you can see normally in darkness, both magical and nonmagical, to a distance of 60 feet for 10 minutes.
Infernal Condition
You are bolstered by aspects of the devil within your blade. While you are wielding your infernal blade, you are resistant to fire damage, but you are vulnerable to radiant damage.
Bully
At level 7, you have started to come to terms with the powers of your blade and the effect it can have on you and on those around you. As an action, you may spend 1 charge from your blade to enhance the most sinister aspects of your appearance. You gain advantage on intimidation checks for 1 minute.
Hellfire Blade
At 7th level, your blade attacks are always considered magical for the purpose of overcoming damage resistance. As a bonus action, you may spend 2 charges from your blade to invoke an incantation that ignites your blade with infernal hellfire. On a successful hit, your blade does an additional 1d6 fire damage. This effect lasts for 1 minute.
Release Soul
At 10th level, you learn how to work with the souls of slain enemies absorbed into your sword. When you absorb a soul, you have 1 minute to touch an ally with your blade as an action and release the soul's energy into them as healing for hit points equal to the CR value of the absorbed soul. No soul under CR 1 provides any healing.
Hellfire Burst
At 15th level, you gain the ability to release an explosive burst of hellfire upon your enemies. As an action, you may spend 5 charges from your blade and point your blade to a location you can see within 150 ft and cause a fireball to explode there.
Infernal Magic
Starting at 18th level, you have access to some rudimentary fire magic. Though you are no spellcaster, your mind comprehends the methods of calling a fire shield or a wall of fire. As an action, you may spend 5 charges from your sword to cast either of these spells.
Your constructive criticism of the subclass itself is always welcome. I'm really looking for a horrible mechanical oversight I've created. I thank you for taking the time to help me out.
EDIT: I have modified a few details and reposted the most recent draft of this subclass.
"Not all those who wander are lost"
Hey! not sure if this is too late, but I've got to say I really like the concept! It's got some good potential though there are a few things i think could be improved slightly I'll work through the draft in order:
The only real issue with this is that it seems like it limits the character too much to only use a longsword, it forces the player into a very narrow play style when compared to other sub-classes of fighter, perhaps changing it so that the character can repeat the ritual to transfer the devil into a new weapon. adding a time period for the ritual will help too, during a long rest should work fine. obviously allowing other weapons aside from longswords means that the damage scaling in the table will need to be very different, so you'd have to play around with different ways of getting it to work.
For the next bit I'll cross out ones i think you should remove and then highlight ones I think you should change, then I'll explain my choices:
OK so the first point ties into my initial one, so I'll skip that one.
My only real change I'd add here is just to add the word 'must' into the description:
For this one, the main issue is that it gets negated later on at 7th level, when the blade counts as being magical, since most creatures that are immune or resistant to slashing are only immune to slashing from non-magical attacks this becomes functionally useless. what you should do instead is to just make the weapon count as magical for the purposes of resistances. this is in line with stuff like the Warlock Pact of the Blade, in which pact weapons count as magical and is also a 3rd level ability so it isn't overpowered either.
the next few are ones I view as being mostly irrelevant, the properties of the longsword mean the first one is already covered in the item description and if you change the Infernal Knight to allow other weapons this becomes unnecessary. The second one clashes too much if only longswords are allowed, as the other fighting styles become useless, Fighters as a whole are designed to use a variety of weapons, the last one is also largely unnecessary, Paladin Deities and Warlock patrons don't restrict Resurrection, the DM can rule it as they like, but the base class shouldn't have to specify that resurrection works.
The main changes for this would be to make the absorption automatic, in combat having to use an action to absorb the soul is a bit of a waste. The Hexblade's Curse for Hexblade Warlocks handles healing by using the Warlock level and the charisma modifier, perhaps something similar might be better. except maybe Strength instead? The reason against using CR is that not everyone builds encounters around it, so people who don't use CR won't be able to use this class effectively;additionally the healing would be fairly weak if it's based on CR. Perhaps granting temporary hit points instead would be a wiser choice. Another option would be to take a set amount of hit points from the enemy for healing, such as a quarter, this is modelled of weapons like Blackrazor which have a similar ability, you could add that at higher levels it does a half instead of a quarter, so it scales nicer. since you won't necessarily be landing killing blows all the time it should be fair.
For this one I'll only cover the text here, the table requires some changes, if you allow for multiple weapons, perhaps the Monk damage table will give some ideas. I think perhaps an HP threshold will work better than a CR system, in addition to the aforementioned issues with CR for class mechanics, CR doesn't scale with individual character level, but for groups, so I think HP is a better indicator of a creature's strength, some high CR creatures are flimsy and are more glass cannons after all. this way there is not hard limit on how strong the sword gets. perhaps adding a flat damage bonus onto the sword that increases as it levels up:perhaps Intervals like: 3-5, 6-8, 9-11, 12-14, 14,15-17, 18-20, with +1d4, +1d6, +1d8,, +1d10, +1d12, etc, would work better?
This was just an example to illustrate the kind of stuff you could do, but it feels like a reasonable progression, play-testing is important here to see whether the level up is either too quick or too slow.
For this I think you just need to remove the highlighted phrase, perhaps you could also allow the ability to increase the range to 120 feet at higher levels? otherwise the player may feel like they don't get strong enough. additionally the level requirement for this isn't mentioned
Same as before, the level requirement isn't mentioned. Additionally for some races this is just a straight nerf, certain dragonborn and Tieflings straight up just get a vulnerability, As far as resistances go fire is ok, but fairly common, so I think you could potentially completely rework this or remove it, maybe make the user resistant to charm effects instead? the user is already in the thrall of a devil after all.
I think a charge for only 1 minute of advantage on intimidation is a bit expensive, consider making it just a flat advantage on Intimidation, maybe Deception too? it matches the devilish themes pretty well. In fact depending on how you change the subclass it may be worth removing the charge system completely? it's up to you of course though.
i think 2 charges or only 1d6 is a bit much, since the infernal blade damage will probably be weaker, it might be worth increasing the damage to 2d6? or decreasing the cost of the 1d6 damage to just 1 charge.
This feels slightly out of place, it makes some sense with how the absorb souls works already, but I feel like this healing is a bit too weak for 10th level, maybe using healing like that for the Absorb Soul modifications would work slightly better. also it's unclear if passing the soul on removes the hit points healed by the Absorb Souls ability, does passing the hit points on transfer them from you to the other character? it is a bit ambiguous as is.
For these two I feel that infernal magic is fine, but 5 charges for a Fireball you only get at 15th level seems a bit much, I think 3 charges is more reasonable, otherwise you can only use that single fireball and nothing else. perhaps making the cost of charges equal the spell level is a fairer way? that means maybe adding a fifth level spell to the Infernal Magic, though that seems reasonable enough to me. also I think using the standard range of fireball is fine, no need to specify the range. one other thing to clarify is what is the Spellcasting DC for the Infernal Knight? Fireball requires a save and as such needs a spell-casting save. 8 + proficiency + constitution might be a good way to go.
Overall I like the flavour of the class and it looks fun to play!, feel free to completely disregard my post, but I also hope you keep it in mind.
Hope this helps somewhat!
No you're not too late at all. Unfortunately, you're replying to a (by this point) much older draft of my subclass. I have tweaked a lot of things... and then I came to the conclusion that as much as I liked it, it's just thematically too similar to a hexblade warlock. Some of the things that seemed less fighter-appropriate are holdovers from when the class was originally envisioned as a paladin subclass. I still have the subclass on the back burner, but I kept the core blade concept and I'm presently working with the blade as a magic item instead. I'll read over your thoughts again when I have a little more time to devote to it and I'll also share what I have, although think by this point, it's probably better suited to the homebrew forum than the fighter forum.
Most importantly, I appreciate you taking the time to look over it and I definitely appreciate your feedback.
"Not all those who wander are lost"
I think gaining health equal to CR has a large falloff as effective healing.
After a lot of consideration, I have decided to abandon this concept as a subclass and instead, I turned it into a magic item. I felt like it was just too one-dimensional for a subclass, but I still enjoyed the mechanics of the blade itself.
Here is the final product.
"Not all those who wander are lost"